Refining titanium-vanadium alloys



REFINING TITANIUM-VANADIUM ALLOYS William W. Gnllett, College Park, Md.,assignor to Chicago Development Corporation, Riverrlale, Md., acorporation of Delaware Application June 20, 1957, Serial No. 666,899

1 Claim. (Cl. 204-64) This invention relates to the preparation of puretites Patent F tanium or pure titanium-aluminum alloys and substantiallyoxygen-free titanium-vanadium alloys made from titanium-vanadium alloysof commercial purity.

Such high purity alloys may be produced by the combination of highlypure metals under especially controlled conditions to preventcontamination during melting, sinter- 3 ing or fabrication. Such highlypure metals are not readily available, and it is therefore advantageousto produce the substantially oxygen-free alloys of my invention by theinitial production of alloys from the readily availableoxygen-containing materials. It should be understood that the alloys towhich I refer as substantially oxygenfree are those containing not morethan .05% oxygen and generally in the range .01-.02% oxygen.

The oxygen content of the alloys of my invention may be determined byvacuum fusion, but I prefer to use the method of electrode potentialmeasurement as set forth in my copending application, Serial No.655,834, filed April 29, 1957, now abandoned.

In the practice of this invention, I utilize the salt bath ice - 2 nickand LHornstein, Industrial Laboratories, Chicago, 111., June 1957.

In carrying out my invention, I comminute the initial alloys by anysuitable method and make such comminuted alloy an anode in anelectrolytic cell having the cell bath'described. I place in the cell aninert cathode.

The cell arrangement and general parameters of operation are thosedescribed in my copending applications.

This particular application to the present invention will be set forthin the examples.

My present invention does not reside in the bath, the cell arrangementor the general method of operation. These are the same as I havepreviously disclosed for titanium alloy refining.

My invention consists in the steps of alloying titanium in a prescribedmanner to obtain the desired anode, passing a direct current from saidanode to an inert cathode to obtain a substantially oxygen-free alloy oftitanium with the desired composition of alloying.

My invention also encompasses the insertion of a foraminous conductingdiaphragm between anode and cathode to intercept the passage of certainmetals from anode to cathode and forming thereon certain substantiallyoxygen-free alloys within the scope of my invention.

I have found that the anodic solution of vanadium from titanium alloysdepends not only on their vanadium content but on the content of certainother elements in the anodic material. The most important of these otherelements are aluminum and oxygen. The anodic solution of vanadium ishindered by aluminum and favored by 1 oxygen. In the presence of smalloxygen contents e.g.,

of my copending application, Serial No. 573,336, filed 1;;

March 23, 1956, now Patent No. 2,817,631, as an electrolyte. Thepreferred bath for the practice of my present invention consists ofsodium chloride and dissolved therein 5% titanium as lower chloride withan average valence of 2.4 and a dissolved sodium content of 2%.

I have found, however, that good results can be obtained with as low as1% dissolved titanium as lower titanium chloride having an averagevalence of 2.05-2.8 and dissolved sodium from .14%. The relationshipbetween these constituents is by no means haphazard. The

following table shows the general relationship between these parameters:

alkaline earth halides other than sodium chloride. may, for example,consist of SrCl 35% NaCl; for best results, however, such a bath shouldcontain 8% dissolved titanium as lower chloride with an average valenceof 2.4 and containing 6% dissolved alkali or alkaline earth metal.

The procedure for determining alkali or alkaline earth metal andtitanium valence in these baths is set forth in a paper entitled TheChemistry of the Reduction of Titanium Chlorides in Fused AlkalinousChlorides by Solutions of Alkalinous Metals by R. S. Dean, L. D. Res

.1.2%, 5% aluminum tends toinhibit vanadium solution from the anodicmaterial. Aluminum, however, dissolves to theextent of about .8% of thetitanium dissolved.

The effect of aluminum up to 6% is overcome by the presence of 3% oxygenso that vanadium, but not aluminum, is anodically dissolved. In eithercase, the cathode produce is substantially free from oxygen.

In the preferred embodiment of my invention, I make an alloy of titaniumcontaining 1% vanadium and 3% oxygen and such amounts of aluminum, iron,nitrogen and carbon as maybe incidentally present. I comminute thisalloy and use it as anode material. Titanium and vanadium are dissolvedfrom the anode material in about the proportions present. The otherelements present in the anode material do not dissolve.

The titanium and .vanadium diffuse as chlorides from the anode towardthe cathode.

My invention consists in providing a layer of pure titanium in thediffusion path. This may be done in several ways. The simplest andpreferred method is to place an iron mesh between anode and cathode.Titanium metal is deposited on this mesh due to its position in the bathwhen current is passed. This titanium metal removes vanadium from thebath substantially quantitatively.

When the process of my invention is carried out in this way, an alloy oftitanium with 3% vanadium is deposited on the titanium coated iron meshin theform of coarse crystal intergrowths, while pure titanium is formedadherent the cathode. v

When the anode material contains less oxygen and more aluminum, 'e.g.,0.5% oxygen, 5% aluminum and 4% vanadium, the solution of vanadium isinhibited and the coarse crystal intergrowths formed on the screencontain 2% vanadium, while those formed on the cathode contain 0.5%aluminum. These intergrowths are substantially oxygen free.

The foraminous divider is merely a means of providing pure titanium inthe diffusion path. The removal of vanadium is chemical notelectrochemical. The vanadium may also be prevented from reaching thecathode by providing a falling stream of pure titanium crystals in theditiusion path in place of the foraminous divider. The crystals may berecovered and re-used until they contain as much as vanadium.

Having now described my invention, I will illustrate it, by examples.

Example I The operation was carried out in an electrolytic cell such asthat described in Figure 1. The cell was made of a covered cylindricalcontainer 1 composed of type 304 stainless steel within which wassupported abasket 2,v composed of concentrically mounted bands of perforated steel with holes spaced on /2" centers. Concentrically mountedwithin the inner annulus of this basket was a screen 3 composed of lowcarbon steel which had 16 mesh to the square inch and concentricallymounted within the steel screen was a central rod 4 composed of mildsteel.

The anode basket was filled with the crushed product of an ingot which.was composed of 5% aluminum, 5% vanadium, 3% oxygen. and 86% titanium.The individual, anode particles were large enough that they would notpass through the perforations in the basket, but did not exceed /2 cubicinch in volume. An inlet 5 and outlet 6 were provided so as to keep the.inside of the container under a flow of inert gas.

The cell bath consisted of 85% by weight of sodium chloride, 13.4% byweight of titanium chloride (4.8% dissolved titanium as lower chloride)in which the average valence of the titanium was 2.5 and. 94% ofdissolved sodium metal. The bath was maintained at a temperature of 850C. by means of electric resistance units surrounding the cylindricalcell container.

External connections were made, so that the basket filled with theparticulate titanium alloy was the anode; the central rod was thecathode. and the screen dividing the anode and cathode was insulatedfrom other, parts of the cell by means of a porcelain tube 7.

A direct current of 50. amperes was passed through cell so thatthere wasan anode current density of 1 am pere/sq. in. and a cathode currentdensity of 100 amperes/sq. in. At the. end of 12 hours, the current wasstopped and the salt drained into another container by melting a frozensalt plug at the drain.

A crystalline material which was scraped from the screen had a particlesize coarser than 30 meshes to the square inch and a composition of 5%vanadium, .03% O balance titanium. A crystalline material was scrapedfrom the cathode which hada particle size coarser than 8 mesh and acomposition of .02%. oxygen, balance titaniurn.

Example II herent the cathode was composed of .02% 0;, balance titanium.

4 Example III The method of Example I was repeated except that thecurrent density on the anode was 50 amp/sq. ft. and the current densityon the cathode was 5000 amps/sq. it. A basket hopper containing finelydivided titanium 8 as shown in Figure 2 was suspended over the screenarea and the screen was not used. By agitating the hopper, a fallingstream of finely divided titanium was caused to pass through theelectrolyte in the approximate area that was previously occupied by thescreen. The resultant cathode product had a composition of .04 O balancetitanium.

Example IV I proceed as in Example I except that I use an anode materialwhich is composed of 5% vanadium, 4% aluminum and 1.5% O

The resultant product scraped from the screen had a composition of 2%vanadium, 2.2% aluminum and .03% oxygen. The product removed from thecathode had a composition of 1.0% aluminum, .02% oxygen, balancetitanium.

Example V In this example I proceed as in Example IV exceptthat I carryout several consecutive runsadding more of the same anode material butusing the same bath. Under these conditions the aluminum chloridecontent of the bath increases. When the aluminum chloride content ofthe-bath increases to more than that corresponding to 1% aluminum, thematerial deposited at the cathode becomes finely divided, and I preferto reduce this aluminum content. In the present example I place the bathunder a reduced pressure of 5 mm. of mercury for a period of 30 minutesduring electrolysis at 850 C. Aluminum chloride distills off andcondenses in the cooler part of the cell from which it is recovered.After this step the bath contains .2% Al as chloride, and issatisfactory for further operation.

What is claimed is:

A process of producing coarse crystal intergrowths of pure titaniumcontaining less than .03% oxygen and a vanadium-titanium alloycontaining O.55% vanadium and less than .03% oxygen which consists inproviding a comminuted titanium alloy anode containing .5-5%

vanadium, 13% oxygen, and incidental amounts of iron, tin, nitrogen,carbon, and aluminum, the aluminum-oxygen ratio being not more than 2,an initial bath of at least one alkalinous chloride having dissolvedtherein 1- 5% titanium as chloride with an average valence of 2.05- 2.8and .l4% dissolved alkalinous metal and an inert cathode, passing adirect current from anode to cathode at a current density of -5000amperes/sq. ft. on the cathode and 1-50 amperes/sq. ft. on the anodematerial and disposing a layer of pure titanium crystals between theanode and cathode so that the titanium and vanadium chlorides arethereby passed through it in diffusing from anode to cathode to formtitanium-vanadium alloy from the layer of titanium crystals by chemicalreaction with the vanadium chloride from the said titanium and formcoarse crystal intergrowths of pure titanium adherent to the cathode.

